Forming injection molded parts by a sandwich or co-injection method has previously been accomplished. One of the techniques currently used for sandwich molding involves injecting a first material into a mold cavity, and subsequently injecting a second material into the mold cavity at the same injection point. The second material displaces the first material so that the second material forms a core of the injection molded part and the first material forms a shell of the injection molded part. Often, the first material is injected through the injection point again after completion of injection of the second material so that the entire exposed outer surface of the injection molded part is formed of the first material. The problem with existing sandwich molding techniques is that the technology that facilitates the injection is extremely expensive and complicated because a single valve gate tip must be capable of being used with multiple different materials at different times. Thus, the valve gate tip must be capable of opening and closing ports to facilitate separate injection of the first and second materials. Thus, a need exists for a simplified method and system for forming injection molded parts, and particularly oral care implements such as toothbrushes, using a sandwich method.